Search

The genus Echinacea (Asteraceae) has importance economically, medicinally, and ornamentally. Endemic to North America, distribution is centered in the states of Arkansas, Kansas, Missouri, and Oklahoma. Native Americans of the central Great Plains used Echinacea as a highly prized medicinal plant panacea. This anatomical study is based on R.L. McGregor's taxonomic treatment of the genus Echinacea that included 11 taxa: E. angustifolia var. angustifolia, E. angustifolia var. strigosa, E. atrorubens, E. laevigata, E. pallida, E. paradoxa var. neglecta, E. paradoxa var. paradoxa, E. purpurea, E. sanguínea, E simulata, and E. tennesseensis. Anatomy of Echinacea tennesseensis was not included because live plants were not available. Plants were collected at the height of anthesis from the experimental gardens at the University of Kansas. Samples were prepared for microtome and free-hand sectioning and staining. Macromorphology and microanatomy are described here, and photomicrographs illustrate the adaxial epidermal cells of ray ligules. Tissue map line drawings illustrate the pattern and distribution of stem trichomes, epidermal cells, cortex, vascular bundles, and pith. Measurements were included for stem diameters, epidermis, collenchyma, parenchyma, xylem vessels, sclerenchyma fibers, xylem and phloem vascularization, protoxylem points, and location and number of secretory canals for each Echinacea taxon. Sclerenchyma fibers (sclerotic cells with a black phytomelanin substance) are located in the pith tissue of all the varieties of E. angustifolia. Tissue maps and photomicrographs illustrate petiole transections and the presence of brachysclerids (stone cells) in E. paradoxa var. neglecta which were found nowhere else in this study. Plants resulting from crossings and introgression between E. atrorubens and E. angustifolia had many intermediate characteristics and were called "race intermedia." This name has no nomenclatural standing but the plants were found to have unique ray ligule adaxial epidermal cells. These multicelluar structures consist of an enlarged basal cell with a neck and a catenuliform series of one, two, or three discrete pyramidal cells that have not been described for any member of the Asteraceae or other flowering plant. A key to Echinacea taxa that includes the distinctive micromorphology of ray ligule adaxial epidermal cells is presented. A discussion of the structure and function of ray ligule microanatomy is included as this relates to insect pollinators. Questions still remain concerning the constancy of anatomical characters over a broad range of habitats based on statistically sampled populations. [ABSTRACT FROM AUTHOR]

Eight new species of Lecideaceae are described from the southern subpolar region: Bryobilimbia coppinsiana Fryday, a saxicolous species with one septate ascospores (Campbell Island, New Zealand); Immersaria fuliginosa Fryday, with a thallus composed of thalloconidia (Falkland Islands); Lecidea aurantia Fryday, with an orange thallus (Auckland Islands, New Zealand); L. campbellensis Fryday, with an endolithic thallus and apothecia resembling those of a species of Porpidia (Campbell Island); Poeltiaria ochyrae Hertel, which is similar to P. subincongua but with a thick areolate thallus (South Orkney and South Shetland Islands); P. tasmanica Fryday, which is similar to P. urbanskyana but with smaller ascopores (Tasmania); Poeltidea inspersa Fryday with an enolithic thallus and a hymenium with large oil globules (Falkland Islands); and Porpidia vulcanoides Hertel & Fryday with immersed apothecia with a thick margin and large ascospores (SW Chile). Lecidea kalbii Hertel is resurrected from the synonymy of L. mannii Tuck. and treated as a distinct species. The circumscription of genera within the Lecideaceae is also discussed: Poeltiaria is shown to be heterogeneous, and the genera Labyrintha and Notolecidea are reduced to synonymy with Poeltidea and Poeltiaria respectively, and the new combinations Poeltidia implexa (Malcolm et al.) Hertel & Fryday and Poeltiaria subcontinua (Hertel) Hertel & Fryday made. A key to the genera of Lecideaceae s. lat. is provided. [ABSTRACT FROM AUTHOR]

Highlights: [•] PCR-based approach alone could not detect S-RNase gene polymorphisms in potato species. [•] In silico PCR assay and restriction enzyme pattern analysis were performed. [•] A novel dichotomous key was developed to discriminate the S-RNase alleles in potato. [•] Experimental data validates the utility and efficiency of the dichotomous key. [Copyright &y& Elsevier]

One new genus and two new nematode species of the subfamily Stilbonematinae are described from phosphorite nodule deposits on Chatham Rise, Southwest Pacific Ocean (350 m water depth). Centonema n. gen. is characterised by finely striated cuticle, absence of cephalic capsule, loop-shaped amphid, pharynx differentiated into swollen anterior procorpus, slender median portion, and round posterior bulb, and the male by sub-ventral and sub-dorsal pairs of thick conical setae (porids) on the tail. Centonema n. gen. most closely resembles Eubostrichus, but differs from the latter in the presence of a tripartite pharynx with swollen procorpus, pairs of sub-dorsal porids on the tail of males, and in the size and shape of its bacterial symbionts. The type and only species of the genus, Centonema renamphidum n. gen et n. sp., is characterised by six sub-cephalic setae with one sub-cephalic seta situated directly posterior to each amphid, spicules with capitulum, gubernaculum with broad dorso-caudal apophyses, and tail of males with three pairs of sub-dorsal and four pairs of sub-ventral porids. Eubostrichus hortulanus n. sp. is characterised by cryptospiral amphideal fovea and spiral amphideal aperture, eight short sub-cephalic setae with two sub-cephalic setae situated directly posterior to each amphid, spicules with capitulum, and a gubernaculum with broad dorso-caudal apophyses, the male by one pair of sub-ventral porids in the pre-cloacal region and three pairs of sub-ventral porids on the tail, and sexual dimorphism in the shape of the tail. A key to all valid species of Eubostrichus is provided. Both species were most common in subsurface sediments (3-5 cm depth), and rare in surface sediments (0-1 cm). This is only the second record for this subfamily in a deep-sea environment; the presence of this taxon on Chatham Rise is likely due to the proximity of the highly productive Subtropical Front and the relatively coarse nature of the sediments. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Both macrofossil and microfossil plant remains from the grass family (Poaceae) have been recovered from Neolithic and historic sites in China. Basing our work on the plant taxa that were previously recovered, we analyzed the economically significant genera for modern starch grain analysis with a focus on the important tribe Triticeae. Modern starch grains from the tribe Triticeae were compared with those from other grasses, and criteria for identification were determined. In total, 38 species within 28 genera, 13 tribes and 4 subfamilies were selected for analysis. Results demonstrate that starch grains from members of the tribe Triticeae are discernible from those of other tribes by their distinctive lenticular morphologies and surficial pressure craters. A dichotomous key covering 10 species within 7 genera of the Triticeae was created, thus allowing identification of members of the tribe to the level of genus. Application of the dichotomous key to the ancient starch assemblage recovered from lithic tools excavated from the early Neolithic site of Donghulin demonstrates that plants from the genera Hordeum and Agropyron were exploited alongside millets at this site. [Copyright &y& Elsevier]

1. Effective management of aquatic fauna requires knowledge of the ways in which populations in different catchments and sub-catchments are connected. A powerful way to estimate this is using genetic markers, which provide information on the average amount of genetic connectivity among populations over generations. Although many studies of genetic connectivity have appeared in the literature, there are innumerable species that have not been studied. 2. This study explores whether it is possible to make broad generalisations about population connectivity, based on readily available information in the form of species life history and architecture of the aquatic habitat. 3. A number of models have been proposed to explain the pattern of connectivity shown by aquatic species with different life-history characteristics, for example, the stream hierarchy model, Isolation by Distance, the Death Valley Model, the headwater model and panmixia. 4. In this study, we propose a dichotomous key to assign species to different models of potential connectivity. The key is based on a few very simple questions about the life history of the species and the geographical arrangement of study sites. We then assessed the performance of the key with 109 data sets of Australian fish and macroinvertebrates, using genetic data to provide an estimate of realised connectivity. 5. The realised connectivity fitted the proposed potential connectivity model in over 70% of cases, and we suggest this might be a useful initial approach for managers where empirical data are lacking. [ABSTRACT FROM AUTHOR]

The male genital sclerites of cockroaches of genus Muzoa Hebard, 1921 are described for first time and the new species Muzoa curtalata sp. n. is described and ilustrated. A dichotomous key to identify the species of genus Muzoa is given. [ABSTRACT FROM AUTHOR]

The subgenus Melanoconion of Culex is a diverse and taxonomically challenging group of mosquitoes (Diptera: Culicidae) endemic to the American tropics, with a few species occurring in temperate regions. With the introduction and establishment of Culex (Melanoconion) panocossa in southern Florida, the existing taxonomic resources for identifying species of Melanoconion in Florida need updating. Here we provide an up-to-date photographic key for identifying females of Culex (Melanoconion) spp. known to occur in Florida, USA, and summarize relevant literature on the biology of each species. Given the challenge of identifying members of subgenus Melanoconion, updated resources for identifying females of this medically important group are warranted. The keys, photographs, and summarized biological information in this report should facilitate research, surveillance, and decisions regarding control., (Copyright © 2022 by The American Mosquito Control Association, Inc.)

Presently the only keys available for identification of genera of Anthonomini are limited to those of the United States of America and Canada. A dichotomous key is presented to identify all genera of Mexican and Central American Anthonomini. Previous keys do not include the genera Achia, Botanebius, Loncophorus, Loncophorellus and Melexerus. A brief synopsis is given for each genus and photographs of representative species are included [ABSTRACT FROM AUTHOR]

The invasive cactus borer Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) now cooccurs with a species of borer native to North America, Melitara prodenialis Walker (Lepidoptera: Pyralidae), in the southeastern United States. Because C. cactorum damages native species of pricklypear (Opuntia) often through population outbreaks, it is necessary to distinguish this species from the native cactus borer that has reduced impact on pricklypear populations. Cactoblastis cactorum and M. prodenialis eggs are laid one on top of another to form eggsticks that resemble cactus spines. Both moth species utilize the same host plant species in the Opuntia genus, and during larval life stages it is easy to distinguish the two species. Determining species identification based on eggs alone, however, has been difficult. Yet, it is impractical to wait for eggs to hatch and larvae to develop to determine species identification for research or monitoring purposes. Several objective, quantitative differences were found between the two species that can be used in laboratory identification to train research assistants or invasive management personnel for the field. Based on the data, we provide a dichotomous key to distinguish the eggsticks of these two species. [ABSTRACT FROM AUTHOR]

To better understand the taxonomy and phylogeny of the genus Omphalodes (Boraginaceae), the pollen morphology of 23 species encompassing all major geographical and morphological groups was studied from acetolysed pollen grains using light and scanning electron microscopy. Three pollen types were distinguishable through apertural morphology and sculpture. A dichotomous key to the pollen types and pollen descriptions are provided. Despite being fairly homogenous, palynological data provided useful information to understand the relationships of Omphalodes, considering the uselessness of most floral and fruit characters, karyological homogeneity and striking disjunct geographical distribution. At the suprageneric level, pollen morphology supports the traditional tribal classification of Omphalodes within Cynoglosseae, in contrast to published molecular phylogenetic analyses. At the infrageneric level, pollen morphology agrees with phylogenetic analyses suggesting that Omphalodes could be a polyphyletic group. Palynological data would support the segregation of a monophyletic group comprising the Japanese species, corroborating recent phylogenetic results and define two different pollen types for the Omphalodes s. str. group. Biogeographical considerations are also discussed. [ABSTRACT FROM PUBLISHER]

We report the discovery of a new species of Lophostoma from Panama, which we name L. kalkoae. This new species resembles L. carrikeri and L. yasuni in possessing a white venter, but is distinguishable from both by external and cranial characteristics. The new species is similar in size to L. carrikeri and L. schulzi. Lophostoma sp. nov. can be most easily recognized by its combination of white venter, postauricular patches connected by a thin line of pale hair to the white fur on the chest, elongated clitoris and swollen labia, less strongly developed lateral projection of mastoid processes, well-marked indentation on the lingual cingulum of the upper canine, well-developed P3, well-developed posterior lingual cusp on the cingulum of P4, and parastyle absent on M1 and M2. We present a dichotomous key for the genus Lophostoma and a map showing all the localities where white-bellied Lophostoma have been recorded. [ABSTRACT FROM AUTHOR]

Fifty-six species or approximately 20% of the Neotropical characiform superfamily Anostomoidea (families Anostomidae, Chilodontidae, Curimatidae and Prochilodontidae) occur in the freshwaters of French Guiana, Guyana, and Suriname although these regions span only approximately 6% of the native range of this morphologically and ecologically diverse superfamily. As a result of the high diversity of anostomoids in the Guianas, the taxonomic and/or geographic boundaries of many species are poorly understood, particularly within the family Anostomidae. This contribution unites results of prior taxonomic revisions with surveys of the holdings of the superfamily in seven major natural history collections to provide distribution maps and keys to the identification of all anostomoid species known to occur in the Guianas. These maps reveal six major areas of endemism: the Takutu and Ireng rivers (Rio Branco drainage, Amazon basin), the Barima and Waini rivers (Orinoco drainage), the Essequibo-Rupununi River system (including the Demerara and Berbice rivers), a union of the Corantijn, Nickerie, Coppename, Saramacca and Suriname river drainages, the Marowijne/Maroni River system (including the Litani and Mana rivers), and the Oyapock-Approuague River basins. Of these, the Essequibo- Rupununi system harbours the most exceptionally diverse assemblage of anostomoid species, likely as a result of faunal exchange between the Rio Branco and Essequibo River across the Rupununi portal. [ABSTRACT FROM AUTHOR]

In this manuscript, external male and female genitalic characters of Amerila eugenia (Fabricius) have been studied and illustrated for the first time. Besides this, a dichotomous key for the separation of all four Indian species of this genus has been provided. [ABSTRACT FROM AUTHOR]

On 27 March 1689, Richard Waller, Fellow and Secretary of the Royal Society presented his "Tables of the English Herbs reduced to such an order, as to find the name of them by their external figures and shapes" to his assembled colleagues at a meeting of the Royal Society. These tables were developed for the novice by being color images, composed in pencil and watercolor, of selected plants and their distinguishing characteristics. The botanical watercolors for the tables are now a Turning-the-Pages document online on the website of the Royal Society. However, for the past 320 years, the scientific context for the creation of these outstanding botanical watercolors has remained obscure. These tables were developed by Waller as an image-based dichotomous key, pre-dating by almost 100 years the text-based dichotomous keys in the first edition of Flora Française (1778) by Jean Baptiste Lamarck, who is generally given priority for the development of the dichotomous key. How these large folio images were arranged to illustrate a dichotomous key is unknown, but an arrangement based on Waller's description is illustrated here as leaf-ordering for the separate hierarchical clusters (tables). Although only 24 species of watercolored dicot herbs out of a total of 65 in the set of watercolors (the others being monocots) are used in these tables, they are a "proof of concept", serving as models upon which a method is based, that of using a key composed of dichotomous choices for aiding identification. [ABSTRACT FROM AUTHOR]

Copyright of Biota Neotropica is the property of Biota Neotropica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the summer of 2009, as an RET (Research Experience for Teachers), I joined the research team studying Echinacea angustifolia by assisting with ongoing research. I also prepared botanical collections for my classroom. These collections consist of flowering botanical specimens and prepared slides of fresh pollen from each plant. Digital images of fresh pollen from these plants were captured to build an online digital pollen library. A portion of the online pollen images serves as an original dichotomous key to be constructed by students in 10th grade Biology. This article describes the field activities of the research team and the process for the plant and pollen collection as well as instructions for the pollen lesson implementation. The national content standards (9-12) for history and nature of science involved are G.1: 'Develop an understanding of science as a human endeavor' and G.2: 'Develop an understanding of the nature of scientific knowledge.' [ABSTRACT FROM AUTHOR]

The article presents research which dealt with the little-known Bolitogyrus Chevrolat species in Mainland China. The researchers collected specimen of male Bolitogyrus kitawakii from the Sichuan Province of Micangshan. They described the body length of the species to be 8.5 millimeters and its mouthparts and antennae to be yellowish brown. They also discovered that it has convex and large eyes as well as its tempora is 0.14 shorter as long as eye in the dorsal view while its legs are moderately slender and long.

The article discusses the discovery of a new species of webspinner also called Eosembia apterosa in the Chiang Mai Province of Thailand. The authors describe the species to have a cranium blackish head and well developed dark eyes. According to them, the prothorax of this species is darkish orange while its metathorax appears to be darkish brown. They also mention that its blackish brown abdomen is slightly and dorsally paler ventrally with the presence of sternites that are medium brown in color.

Plant compensatory growth is a phenomenon of exaggerated vegetative growth that occurs in plants as a result of mechanical damage (e.g., cutting or browsing). Because shoots, leaves, and other plant parts grow larger on plants undergoing compensation, they typically fall outside of the normal ranges given in plant identification keys and confuse students who are attempting to classify them. Here, we describe the conundrum faced by students collecting compensatory materials and offer suggestions on how to help students identify their 'plant-in-hand' and how to seize a teaching moment to examine and explain the underlying processes that lead to this fascinating plant response. [ABSTRACT FROM AUTHOR]

The article discusses a taxonomic study of Aleochara (Aleochara) kochi Bernhauer identified in the Korean peninsula with illustrations of its habitus and diagnostic morphological characters. The Korean specimens studied were deposited at the Chungnam National University Insect Collection in Korea. It redescribes the species as body brown, antennae and legs yellowish brown. This species have minute b-setae on the apical portion of the labrum and differs from other members of subgenus Aleochara by having more elongate and more acute ligula.

Two new thick-tail scorpions in the genus Parabuthus Pocock, 1890 are described from the gravel plains of the Central Namib Desert, Namibia: Parabuthus glabrimanus sp. nov.; Parabuthus setiventer sp. nov. The two new species occupy discrete distributional ranges, allopatric with the closely related species Parabuthus gracilis Lamoral, 1979 and Parabuthus nanus Lamoral, 1979. The distributions of the four species are mapped and a key provided for their identification. Revised diagnoses are provided for P. gracilis and P. nanus. The two new species are added to a previously published morphological character matrix for Parabuthus species and their phylogenetic positions determined in a reanalysis of Parabuthus phylogeny. Parabuthus setiventer sp. nov. is found to be the sister species of P. nanus, whereas P. glabrimanus sp. nov. is sister to a monophyletic group comprising P. gracilis, P. nanus, and P. setiventer sp. nov. The discovery of two new scorpion species endemic to the Central Namib gravel plains contributes to a growing body of evidence that this barren and desolate region is a hotspot of arachnid species richness and endemism. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159, 673–710. [ABSTRACT FROM AUTHOR]

A checklist and dichotomous key to 128 species of bats known from South Asia including Afghanistan, India, Pakistan, Nepal, Bhutan, Bangladesh, Sri Lanka and Maldives is provided. Character matrices for families, genera and species are also included. This article also briefly reviews their distribution (both physiographic and country-wise), status and main identification characters. [ABSTRACT FROM AUTHOR]

Species identification is a necessary component of most studies of biological diversity, and computational approaches are beginning to automate it. In particular, leaves of plants provide taxon-specific information that has successfully been applied to plant identification. Prior studies have not investigated the number of leaves or the resolution of the digitized leaf image required to represent a species' shape. Moreover, the relationship between accuracy and the size of the leaf shape database, and methods to integrate automated approaches with more traditional dichotomous keys have yet to be explored. Here, I use a database of 2,420 leaves from 151 species to address these issues. Using distance metrics derived from Fourier and Procrustes analyses, it is found that a minimum of 10 leaves of each species, 100 margin points, and 10 Fourier harmonics are required to accurately represent leaf shape of a species. These results are used to assess the success of species identification from images of leaves: 72% for all 151 species. The tight relationship between database size and accuracy is then used in conjunction with results from probability theory to predict accuracy of species identification when dichotomous multiple-entry keys and combined Fourier and Procrustes analysis are used together. Combining these two approaches to identification can greatly improve identification accuracy. Open-source software is available to implement the automated distance-based approach. [ABSTRACT FROM AUTHOR]

Quantitative behaviour analysis requires the classification of behaviour to produce the basic data. This can be challenging when the theoretical taxonomy does not match observational limitations, or if a theoretical taxonomy is unavailable. Binary keys allow qualitative observation to be used to modify a theoretical taxonomy to produce a practical classification method, or to develop a pragmatic taxonomy in the absence of theory. Furthermore, inter-observer consistency can be maximized with less training, and construction of a binary key ensures that the categories into which behaviour is classified are complete and mutually exclusive. We give examples from special education research for the behaviour of children with developmental disabilities. [ABSTRACT FROM AUTHOR]

A new species, Gloiocephala cerkezii, is described from Croatia. It is characterized by a pale brown to rusty brown pileus, an elongated central to slightly eccentric stipe, vein-like lamellae, large and elongate spores, subcapitate to capitate cystidia, a gelatinized trama, and the absence of hairs on the pileus and stipe. The description is accompanied by black and white photograph of basidiocarps and line drawings of microscopic elements. G. cerkezii is compared to closely related species, and a dichotomous key to European species of the genus Gloiocephala is provided. A new combination Gloiocephala pseudocaricis is made. [ABSTRACT FROM AUTHOR]

A reference karyotype is presented for loblolly pine (Pinus taeda L., subgenus Pinus, section Pinus, subsection Australes), based on fluorescent in situ hybridization (FISH), using 18S-28S rDNA, 5S rDNA, and an Arabidopsis-type telomere repeat sequence (A-type TRS). Well separated somatic chromosomes were prepared from colchicine-treated root meristems, using an enzymatic digestion technique. Statistical analyses performed on chromosome-arm lengths, centromeric indices, and interstitial rDNA and telomeric positions were based on observations from 6 well-separated metaphase cells from each of 3 unrelated trees. Statistically, 7 of the 12 loblolly pine chromosomes could be distinguished by their relative lengths. Centromeric indices were unable to distinguish additional chromosomes. However, the position and relative strength of the rDNA and telomeric sites made it possible to uniquely identify all of the chromosomes, providing a reference karyotype for use in comparative genome analyses. A dichotomous key was developed to aid in the identification of loblolly pine chromosomes and their comparison to chromosomes of other Pinus spp. A cytomolecular map was developed using the interstitial 18S-28S rDNA and A-type TRS signals. A total of 54 bins were assigned, ranging from 3 to 5 bins per chromosome. This is the first report of a chromosome-anchored physical map for a conifer that includes a dichotomous key for accurate and consistent identification of the P. taeda chromosomes. [ABSTRACT FROM AUTHOR]

Two species of Prosopis, Prosopis juliflora and Prosopis pallida, native to Central America and northern South America, have been widely introduced and are now found throughout the world’s hot arid and semi-arid zones. However, these species are frequently misidentified, especially where introduced, hampering genetic improvement and effective management. Samples from trees previously identified as either P. juliflora or P. pallida were divided into two groups by multivariate analysis using selected foliar characters. One group contained known tetraploids and the other contained known diploids. It was concluded that the tetraploid and diploid groups correspond to P. juliflora and P. pallida, respectively. Triploid individuals were also identified, the first report of these in the genus Prosopis. A dichotomous key was developed to differentiate the species, using number of interfoliar glands per rachis, number of leaflet pairs per pinna and leaflet length. P. juliflora and P. pallida grown from seed collected within their respective native ranges were correctly identified using the key. Where introduced, samples from Burkina Faso, Jordan and India were confirmed as P. juliflora, but those from Brazil, Cape Verde and Senegal were identified as P. pallida, rather than P. juliflora, the species assumed to be naturalized in these countries. The correct identification of these two species will facilitate the genetic improvement and management of P. juliflora and P. pallida. There is a strong case for basing future selection and genetic improvement programs on P. pallida rather than P. juliflora. Further collection and evaluation of P. pallida is therefore required, together with conservation programs in the native range. [Copyright &y& Elsevier]

Species of the nematode genus Heterorhabditis are important biological control agents against agricultural pests. The taxonomy of this group is still unclear as it currently relies on phylogenetic reconstructions based on a few genetic markers with little resolutive power, specially of closely related species. To fill this knowledge gap, we sequenced several phylogenetically relevant genetic loci and used them to reconstruct phylogenetic trees, to calculate sequence similarity scores, and to determine signatures of species- and population-specific genetic polymorphism. In addition, we revisited the current literature related to the description, synonymisation, and declaration as species inquirendae of Heterorhabditis species to compile taxonomically relevant morphological and morphometric characters, characterized new nematode isolates at the morphological and morphometrical level, and conducted self-crossing and cross-hybridization experiments. The results of this study show that the sequences of the mitochondrial cytochrome C oxidase subunit I (COI) gene provide better phylogenetic resolutive power than the sequences of nuclear rRNA genes and that this gene marker can phylogenetically resolve closely related species and even populations of the same species with high precision. Using this gene marker, we found two new species, Heterorhabditis ruandica n. sp. and Heterorhabditis zacatecana n. sp. A detailed characterization of these species at the morphological and morphometric levels and nematode reproduction assays revealed that the threshold for species delimitation in this genus, using COI sequences, is 97% to 98%. Our study illustrates the importance of rigorous morphological and morphometric characterization and multi-locus sequencing for the description of new species within the genus Heterorhabditis , serves to clarify the phylogenetic relationships of this important group of biological control agents, and can inform future species descriptions to advance our efforts towards developing more tools for sustainable and environmentally friendly agriculture., (© 2021 Authors.)